1. Field of the Invention
The present invention relates to an eye examining apparatus for effecting eye examination by selectively changing over the refractive power of a lens.
2. Related Background Art
Eye examining apparatuses for finding the optimum degrees of spectacles are well known. An eye examining apparatus effects not only the measurement of the degree of eye refraction, the degree of astigmatism and the axial direction of the human eye, but also the measurement of examination of presbyopia, heterophoria, vergence, divergence and balance of both eyes. To make these examinations possible, the eye examining apparatus according to the prior art has an optical system of such structure as shown of on FIG. 1 of the accompanying drawings. FIG. 1 shows an optical system in the eye examining apparatus for measuring only one of left and right eyes. The actual eye examining apparatus provides two optical systems as shown in FIG. 1 and effects the examination of left and right eyes. In FIG. 1, reference numeral 1 designates an auxiliary lens plate, reference numeral 2 denotes a second spherical lens plate, reference numeral 3 designates a first spherical lens plate, reference numeral 4 denotes a second cylindrical lens plate, reference numeral 5 designates a first cylindrical lens plate, reference numeral 6 denotes an accessory lens, reference numeral 7 designates a rotatable prism, reference numeral 8 denotes a mabdox rod, reference numeral 9 designates a cross cylinder, and reference numeral 10 denotes an eye examining lens chamber. The members 7, 8 and 9 will hereinafter be referred to as the auxiliary magnifiers. The eye examining lens chamber contains therein several disks having a number of eye examining lenses planted thereon as shown in FIG. 1. The auxiliary lens plate 1 (having a prism, a pin-hole, etc.), the second spherical lens plate 2, the first spherical lens plate 3 (for measuring distance visibility), the second cylindrical lens plate 4 and the first cylindrical lens plate 5 (for measuring the degree of astigmatism) overlap one another from the examinee side, and an arbitrary combination of these can be quickly brought out to an eye examining window by rotating the disks having the eye examining lenses planted thereon. The total degree of diopter may be displayed by a simple calculation.
The aforementioned three measuring plates called the auxiliary magnifiers are installed on the front face of the eye examining window, and they can be moved into and out of the window simultaneously or one by one. Reference numeral 7 designates a rotatable prism for measuring heterophoria, and this prism continuously provides a variation in declination by the rotation of two prisms in opposite directions. The mabdox rod 8 is used for the measurement of heteropheria. The cross cylinder 9 comprises, for example, the area of cylindrical lenses of .+-.0.25 diopter made orthogonal to each other, and is a very useful device for the precise measurement of astigmatism, the determination of presbyopia and other purposes. By the apparatus of the construction as described above, it is possible to measure the farsightedness and near-sightedness (the degree of sphericity), astigmatism, astigmatic axis, heterophoria, vergence, divergence, pupil distance etc.
In the prior art, however, a number of eye examining lenses are prepared from the necessity of coping with diversified visual powers and it is necessary to change these lenses in succession. This has led to a bulky expensive and cumbersome apparatus. Also, the large degree of mechanical movement during the change-over has led to the disadvantage that much time is required for the change-over. Since a number of eye examining lenses are interchangeably set in a limited installation space, the lens aperture of the eye examining lenses must avoidably be made small, and this has led to the disadvantage that so-called mechanical myopia is liable to occur.
Furthermore, in the prior art, a number of lenses have been set in the direction of the optic axis and therefore, even if a predetermined one of these lenses is changed over at a predetermined step (e.g. of 0.25 diopter each) to vary the refractive power thereof, the refractive power is not varied at the step of 0.25 diopter since as the whole system is provided with a number of lenses.
Also, in the prior art, a predetermined eye examining lens is entirely eliminated during the changeover, and this may lead to the possibility that the adjustment power of the eye to be examined will change.